MDT information-reporting format in a wireless communication system, and time-stamp configuring method and apparatus

ABSTRACT

A method for configuring a Minimization of Drive Test (MDT) information reporting format and a time-stamp is provided that supports MDT in a 3rd Generation Partnership Project (3GPP) system. The method defines a reporting format needed in a process where UE transmits MDT measurements to a serving base station, and sets the number of bits required to log time stamp and the unit of logging time.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of a prior applicationSer. No. 13/817,780, filed on Feb. 19, 2013, which was a U.S. NationalStage application under 35 U.S.C. § 371 of an International applicationfiled on Aug. 10, 2011 and assigned application numberPCT/KR2011/005814, which claimed the benefit under 35 U.S.C § 119(a) ofa Korean patent application filed on Aug. 16, 2010 in the KoreanIntellectual Property Office and assigned Serial number 10-2010-0078598,the entire disclosure of each of which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a Minimization of Drive Test (MDT) informationreporting format and a time stamp configuring method to support a MDTfunction in wireless communication systems, or 3rd GenerationPartnership Project (3GPP) systems.

The method defines a reporting format needed in a process where userequipment (UE) transmits MDT measurements to a serving base station, andsets the number of bits required to log time stamp and the unit oflogging time.

2. Description of the Related Art

Mobile communication systems have been developed to providecommunication services to users while they are moving. With the rapiddevelopment of communication technology, mobile communication systemshave provided rapid data communication services as well as voicecommunication services. The specification for Long TermEvolution-Advanced (LTE-A), one of the next generation mobilecommunication systems, is being standardized by the 3GPP. Thestandardization for LTE-A is proceeding to be completed by the latterhalf of 2010. LTE-A refers to a technology that can provide packet-basedcommunication with a higher transmission rate than the current datatransmission rate.

As the 3GPP standardization is evolved, convenient optimizations forwireless networks are being discussed other than increases incommunication service speed. When establishing wireless networks at theinitial stage or optimizing networks, base stations or base stationcontrollers must collect wireless environment information for their cellcoverage, which is called a ‘drive test’. Conventional drive tests areexecuted in such a way that engineers load measurement devices on avehicle and repeatedly perform a measurement task for a relatively longperiod of time, which is complicated. The measurement results areprocessed in analysis processes and they are used to set systemparameters of each of base stations or base station controllers.Conventional drive tests increase in wireless optimization cost andmanagement cost and consume significant time. Therefore, in order tominimize drive tests and to improve analysis processes for wirelessenvironments and manual setting processes, a study called ‘Minimizationof Drive Test (MDT)’ is made. To this end, instead of performing DriveTest, UE measures a channel quality and transmits measurements regardinga corresponding wireless channel to a base station periodically orimmediately when an event occurs. Alternatively, after a certain periodof time has elapsed from the storage of wireless channel measurements,UE may transmit measurements regarding a corresponding wireless channelto a base station. In the following description, the transmission ofwireless channel measurements measured by UE and additional informationto a base station is called an MDT measurements reporting operation. Inthis environment, if UE is capable of communicating with a base station,it can immediately transmit the channel quality measurement result tothe base station. On the contrary, if UE isn't capable of performing animmediate report, it logs MDT measurements and then reports, when it cancommunicate with the base station, the information to the base station.The base station uses the received MDT measurements to optimize cellcoverage. LTE-A classifies types of MDT measurements reporting,according to UE RRC states, as the following table 1.

TABLE 1 UE RRC state MDT measurements reporting by UE Idle mode Loggingand deferred reporting Connected mode Immediate reporting

As described in table 1, ‘idle mode’ refers to a state where UE is notcommunicating with a base station, and ‘connected mode’ refers to astate where UE is communicating with a base station. While MDT isperformed, channel quality information measured by UE can be transmittedvia RRC signaling. Therefore, although UE operates in an idle mode, itcan switch the idle mode to a connected mode in order to transmitcorresponding information. In that case, UE logs channel measurementsand defers the transmission to a base station until its idle mode isswitched to a connected mode.

MDT measurements are transmitted to the base station by the use ofcontrol plane protocol stacks for processing RRC and NAS signals.

FIG. 1 illustrates a general control plane protocol stack of an LTEsystem. RRC layers 105 and 155 perform system information transmission,RRC link control, channel measurement control, etc. PDCP 110 and 150compress/decompress IP header. RLC 115 and 145 reconfigure PDCP PDU inproper size and perform an ARQ operation. MAC 120 and 140 connect to anumber of RLC devices configured in one user equipment. MAC 120 and 140multiplex RLC PUDs to MAC PDU, and de-multiplex RLC PDUs from MAC PDU.The protocol layer devices include proper headers at need. For example,RLC device adds an RLC header including a serial number, etc., to RLCSDU. MAC device adds an MAC header including an RLC device identifier,etc., to MAC SDU. Physical layers (PHY) 125 and 135 in UE and ENBchannel-code and modulate MAC PDU, create OFDM symbols, and transmitthem via a wireless channel 130. PHY 125 and 135 demodulate andchannel-decode OFDM symbols received via a wireless channel 130, andtransfer them to the upper layers. PHY 125 and 135 also perform HybridAutomatic Retransmission request (HARQ) for MAC PDU. HARQ performsretransmission on PHY layer and is a soft combination of a retransmittedpacket and the original packet.

As shown in FIG. 2, MDT measurements logged by UE is transferred fromRRC layer to PDCP layer via Signaling Radio Bearer 2 (SRB2). RRC controlmessage or NAS message 210 is transferred from RRC layer 205 to PDCPlayer 230 via SRB0 (215), SRB1 (220) or SRB2 (225). SRB0 is used totransfer RRC message via CCCH. SRB0 has the highest priority order. SRB1is used to transfer RRC message via DCCH, and also NAS message part ofwhich is transferred in piggyback format. SRB2 is used to transfer NASmessage via DCCH. The packets transferred by SRB1 and SRB2 are allencoded via integrity and ciphering processes. SRB1 has a higherpriority order than SRB2. MDT measurements are transferred via SRB2 withthe lowest priority order. User plane data can be also transferred viaData Radio Bearer (DRB) 250 other than SRB0˜SRB2. Packets transferredvia DRB are processed by a ciphering and ROHC process 255 andtransferred to RLC layer 265. RLC layer maps corresponding packets toDTCH.

UE operating in idle mode logs MDT measurements periodically or when themeasured information meets a specific event. An example of an event forlogging MDT measurements is as follows.

-   -   (1) Periodical downlink pilot measurements    -   (2) Serving Cell becomes worse than threshold    -   (3) Transmit power headroom becomes less than threshold        Logged MDT Measurements:    -   (1) Global cell ID of a serving cell    -   (2) Measurements regarding Reference Signal Received Power        (RSRP) and Reference Signal Received Quality (RSRQ) of a serving        cell    -   (3) Location information    -   (4) Time stamp

MDT measurements need to include information to identify a serving cell,i.e., global cell ID. This tells which cell corresponding information isacquired. A global cell ID must uniquely indicate one cell. A wirelesschannel state of a serving cell can be expressed via a specificmeasurement. The states of EUTRA can be expressed via RSRP and RSRQ,UTRAN via RSCP and Ec/No, and GERAN via Rxlev. The embodiments of theinvention are described based on EUTRA LTE systems; however, it shouldbe understood that the invention can also be applied to the othersystems. In 3GPP, the MDT function will be applied to LTE and UMTS.

Location information from among MDT measurements transmitted to a basestation serves as an important component. If UE can't acquire theGPS-based location information, it measures a set of Reference SignalReceived Power from the adjacent base stations and informs the basestation of it. The set of Reference Signal Received Power is called a RFfingerprint. Since the base station receiving the RF fingerprint hasknown the location information regarding the adjacent base stations, itapplies the signal power values of the adjacent base stations to asignal path attenuation model and thus predicts the distances betweenthe UE and the respective, adjacent base stations. If the locationinformation regarding the adjacent base stations and the predicteddistances between the UE and the adjacent base stations are applied to atechnique, such as a triangulation, an approximate location of the UEcan be acquired. If UE isn't capable of acquiring the GPS-based locationinformation, it can acquire information regarding a predicted locationinstead of an accurate location and transmit it to the base station.

Time stamp is also important to acquire MDT measurements. When wirelesschannel measurement is performed, time stamp serves to optimize servicecoverage. This is because wireless channel states vary according tohours. Time stamp is more importantly used in a logging and deferredreporting operation in an idle mode than an immediate reportingoperation in a connected mode. Since an immediate report in a connectedmode is going to include a result measured immediately before thereporting operation, time stamp isn't important in the immediatereporting operation in a connected mode. However, if a logging anddeferred reporting operation in an idle mode doesn't use time stamp, itcan't be predicted when the measurement was performed. Therefore, thecurrently developed 3GPP standard doesn't have time stamp for animmediate reporting operation in a connected mode; however, it includestime stamp as necessary information in a logging and deferred reportingoperation in an idle mode.

Time stamp can be provided in various types. Types of time stamps referto an absolute time or a relative time that UE can provide. An absolutetime needs a number of bits to report a corresponding time stamp. On thecontrary, a relative time may need a relatively small number of bitsthan the absolute time.

In the 3GPP standard, relative time stamp is included in MDTmeasurements in order to reduce signalling overhead. When base stationsprovide reference information regarding absolute times to UEs, the UEsinclude relative time stamps in respective measurement samples, based onthe received absolute times. After completing MDT measurement, UEreports the logged measurements to a base station and also informs thebase station of the absolute time reference information that it hasreceived from the base station. This is because a base station thatprovided absolute time reference information to UE at the initial stagemay differ from a base station that the UE intends to make a report to.

FIG. 3 illustrates a flow chart describing a method for performing MDTmeasurement in a logging and deferred reporting operation in an idlemode. eNB 305 configures MDT measurement and transmits correspondinginformation, i.e., MDT measurement configuration information to UE 300in a connected mode (310). The MDT measurement configuration informationincludes absolute time reference information, sampling cycle,measurement duration, etc. The absolute time reference information hasbeen already described above. The sampling cycle is used for periodicaldownlink pilot measurements, and also used to measure wireless channelsat each cycle. The measurement duration refers to the total period oftime in performing MDT. UE performs MDT until a correspondingmeasurement duration has elapsed.

If the RRC connected state of UE 300 with the eNB 305 is switched from aconnected mode to an idle mode, the UE 300 starts to perform MDTmeasurement (315). UE 300 measures and logs MDT (320), and thencontinues measuring and logging MDT at the sampling cycle that wasreceived (325). MDT measurements are logged at each measurement cycle(330).

If UE 300 enters a connected mode (335), it informs the eNB 305 as towhether it has logged MDT measurements (340). eNB 305 may request areport from the UE 300 according to a corresponding state. If UE 300receives the request from eNB 305, it reports the MDT measurements thatit has logged by the time to the eNB 305, and then removes it. On thecontrary, if UE 300 doesn't receive the request from eNB 305, it retainsthe logged information. If UE 300 enters an idle mode but themeasurement duration hasn't elapsed (345), it continues to perform MDTmeasurement and acquires the MDT measurements (350). Measurementduration may or may not take a period of time in a connected mode intoaccount. If the measurement duration has elapsed (355), UE 300 stops MDTmeasurement.

UE 300 enters a connected mode (360). UE 300 informs the eNB 305 thatthere is a newly logged MDT measurement, and reports, if the request ismade from the eNB 305, it to the eNB 305 (365).

However, in order to efficiently transmit MD measurements from UE toeNB, the MDT information reporting format to the eNB and the time stampconfiguration must be defined.

SUMMARY OF THE INVENTION

The invention has been made in view of the above problems, and providesa method and system for configuring a Minimization of Drive Test (MDT)information reporting format and a time-stamp that supports MDT in amobile communication system.

The invention further provides a method and system that defines areporting format needed in a process where UE transmits MDT measurementsto a serving base station, and sets the number of bits required to logtime stamp and the unit of logging time.

In accordance with an exemplary embodiment of the invention, theinvention provides a method for transmitting channel measurements fromUE to an eNB in a wireless communication system, including: receivingchannel measurement setting information from the eNB; measuring wirelesschannel information at cycles included in the channel measurementsetting information; logging the measured wireless channel informationusing a preset time stamp; and transmitting the logged wireless channelinformation to the eNB.

In accordance with another exemplary embodiment of the invention, theinvention provides User Equipment (UE) that measures wireless channelinformation and transmits it to an eNB in a wireless communicationsystem, including: a transceiver for receiving channel measurementsetting information from the eNB and transmitting created channelmeasurements to the eNB; and a controller for: measuring wirelesschannel information at cycles included in the channel measurementsetting information; logging the measured wireless channel informationusing a preset time stamp; and transmitting the logged wireless channelinformation to the eNB.

Preferably, the time stamp has fixed values. The time stamp is stored ina bit field, and the size of bit field is fixed.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will become more apparentfrom the following detailed description viewed in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a general control plane protocol stack of an LTEsystem;

FIG. 2 illustrates a view showing an SRB mapping relation in an LTEsystem;

FIG. 3 illustrates a flow chart describing a method for performing MDTmeasurement in a logging and deferred reporting operation in an idlemode;

FIG. 4 illustrates a reporting format of logged MDT measurements;

FIG. 5 illustrates a flow chart describing a method for operating UE inembodiment 1 of the invention;

FIG. 6 illustrates a flow chart describing a method for operating UE inembodiment 2 of the invention;

FIG. 7 illustrates a first view describing an operation of timeinformation and time stamp unit calculated in embodiment 3;

FIG. 8 illustrates a second view describing an operation of timeinformation and time stamp unit calculated in embodiment 3;

FIG. 9 illustrates a flow chart describing a method for operating UE inembodiment 3 of the invention;

FIG. 10 illustrates a flow chart describing a method for operating UE inembodiment 4 of the invention; and

FIG. 11 illustrates a schematic block diagram showing UE according to anembodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The invention relates to a Minimization of Drive Test (MDT) informationreporting format and a time-stamp configuring method to support a MDTfunction in 3^(rd) Generation Partnership Project (3 GPP) systems.

The method defines a reporting format needed in a process where userequipment (UE) transmits MDT measurements to a serving base station, andsets the number of bits required to log time stamp and the unit oflogging time.

FIG. 4 illustrates a reporting format of MDT measurements logged in UE.The reporting format includes a header 400 and a set of MDT measurements405 collected at a specific time.

The header 400 includes one or a number of pieces of information asfollows.

Echoed absolute time: it refers to a reference time to use a relativetime stamp and UE informs eNB of it when reporting MDT measurements tothe eNB.

Sampling cycle: it is used for an event for logging MDT measurementsperiodically

Measurement type: it is a field indicating a time for periodic MDTmeasurement or specific measurement

Each sample in MDT measurements includes one or a number of pieces ofinformation as follows.

-   -   IE indicators: they indicate whether respective configuration        information items (i.e., relative time stamp, global cell ID,        RSRP/RSRQ measurement, and location information) are in a sample    -   global cell ID of a serving cell    -   RSRP and RSRQ measurements of a serving cell    -   relative time stamp    -   location information

As relative location information, a relative time stamp can be expressedvia a unit of a specific period of time. For example, if Value 1, as arelative time stamp, is defined as 1.28 sec, a relative time can beexpressed as multiples of 1.28 seconds. An MDT measurement devicemeasures channel states according to an actual sampling cycle, and maylog the measurement results by using the time stamp.

The unit of a relative time stamp may also be defined as a fixed time,and also defined considering the number of bits representing timeinformation. For the two examples, the invention proposes a method forderiving the number of bits required to represent time information, amethod for determining a span of time corresponding to one unit of atime stamp, and a method for operating UE.

Embodiment 1

In the embodiment, a span of time corresponding to one unit of timestamp (hereinafter called a ‘time stamp unit’) can be fixed, and a sizeof bit field for storing time information (hereinafter called a ‘timeinformation field’) can also be fixed. For example, if a time stamp unitis 1.28 seconds (preferably, 1 second), the size of a time informationfield to express 3 hours, as a measurement duration, needs 13 bits. Itis preferable that a time stamp unit is set to be identical to asampling cycle. If one time stamp unit is set to 1.28 seconds and thesize of a time information field is set to 13 bits, the design of theembodiment is simple but inefficient. This is because, if themeasurement duration is less or greater than 3 hours, all the bits inthe time information fields are not used. This may waste the timeinformation fields or cause a state where a precise time cannot beinformed. For example, if the measurement duration is 1.5 hours, thenumber of bits for actual time information may be approximately a halfof 13 bits. On the contrary, if the measurement duration is 4 hours, thetime information cannot be expressed by 13 bits. Since the actualmeasurement duration may be configured with a variety of valuesdepending on situations, this can be specifically processed when timestamp value is recorded in the time information field. If one time stampunit is set to 1.28 seconds and the time information field is set to 13bits, the span of time expressed by 13 bits may be approximately 3hours. If the measurement duration is less than 3 hours, the bits notused are processed as ‘zero.’ On the contrary, if the measurementduration is greater than 3 hours, the time information field can beprocessed by a variety of methods. A first method is to reset the timestamp to a value of time stamp 1 (i.e., the first time stamp value) if atime information field doesn't have any available bits to express ameasurement duration. In that case, an eNB needs to perform a procedurethat discerns between a sample having a value of time stamp 1 at thefirst stage and a sample that processes a value of current time stamp 1.Since samples will be recorded in order, samples that are earlierreceived or decoded are regarded as early recorded samples.

A second method is to re-use, if the measurement duration exceeds arange of time that can be expressed by a time information field, ignoresthe excess and reuses the final time stamp value. This is because thetime information field cannot express a time greater than the range oftime. Therefore, eNB must set the measurement duration at the initialstage by taking the condition into account.

FIG. 5 illustrates a flow chart describing a method for operating UE inembodiment 1 of the invention.

UE receives echoed absolute time, measurement duration, and samplingcycle from eNB via MDT configuration information (500). When UE switchesthe current mode to an idle mode, it performs MDT measurement (505). UEdetermines whether the sampling cycle arrives (510).

If a time point arrives to log the measurement result at step 510, UEcollects information items to be logged in samples via the followingsteps 515 to 530. If the MDT measurements are logged according to aspecific event, UE directly perform step 515 without performing step510.

Steps 515 to 530 are described in detail as follows.

UE acquires identification information for identifying serving cells,i.e., a global cell ID (515). After that, UE measures a wireless channelstate (520). In the embodiment of the invention, UE can measure RSRP andRSRQ. UE acquires the location information (525), and determines acurrent time stamp value based on a preset time stamp unit and theabsolute time (530). UE determines whether the size of time informationfield can express the current time stamp information (535). If UEascertains that the size of time information field can express thecurrent time stamp information at step 535, it logs the time stampinformation in the time information field (540). On the contrary, if UEascertains that the size of time information field cannot express thecurrent time stamp information at step 535, it resets the latest timestamp information or the time stamp value and records information from 1(545). UE logs the last collected MDT measurement in one sample (550).UE determines whether the measurement duration has elapsed (555). If themeasurement duration has elapsed at step 555, UE stops the MDTmeasurement. On the contrary, if the measurement duration has notelapsed at step 555, UE waits for the next sampling cycling and returnsto step 515.

Embodiment 2

The embodiment is implemented in such a way that the time stamp unit isfixed and the size of time information field is set to be variableaccording to the measurement duration. The time stamp unit is set to acertain value. It is preferable that the time stamp unit is identical tothe sampling cycle. The value of the time information field varies themeasurement duration configured by eNB. In that case, UE can receivecorrectly the time information field from the eNB. Alternatively, UE cancalculate the time information field based on the measurement durationand the time stamp unit. The size of the time information field iscalculated by the following equation 1.Ceiling{log 2(measurement duration/time stamp unit)}For example, if it is assumed that the time stamp unit is a samplingcycle, the time information field needs the size as follows.Sampling cycle is 5.12 s and the measurement duration is 3600 seconds,relative time field size is 10 bitsSampling cycle is 10.24 s and the measurement duration is 2400 seconds,relative time field size is 8 bits   Equation 1

The size of time information field can be calculated in eNB or UE. Thisis because the time stamp unit is a value that can be set according to acertain assumption and the measurement duration is a value that eNBprovided to UE. Therefore, UE and eNB can have information forcalculating the size of time information field. Thus, eNB can calculatethe size of time information field and inform UE of it. Alternatively,UE can calculate the size of time information field via correspondinginformation transmitted from eNB.

FIG. 6 illustrates a flow chart describing a method for operating UE inembodiment 2 of the invention.

UE receives echoed absolute time, measurement duration, and samplingcycle from eNB via MDT configuration information (600). UE determinesthe size of the time information field by using the measurement durationand the time stamp unit (605). It is preferable that the time stamp unitis identical to the sampling cycle. In that case, UE can determine thesize of time information field via equation 1.

Although the embodiment is implemented in such a way that UE calculatesthe size of time information field, it can be modified in such a waythat eNB calculates the size of time information field and provides itto the UE.

UE switches the current mode to an idle mode and performs MDTmeasurement (610). UE determines whether the sampling cycle arrives(615). If a time point arrives to log the measurement result at step615, UE collects information items to be logged in samples via thefollowing steps 620 to 635. Since steps 620 to 635 are identical tosteps 515 to 525 in FIG. 5, the detailed description is omitted. If theMDT measurements are logged according to a specific event, UE maydirectly perform step 620 without performing step 615. UE logs the timestamp information in the time information field (640), and the lastcollected MDT measurement in one sample (645). UE determines whether themeasurement duration has elapsed (650). If the measurement duration haselapsed at step 650, UE stops the MDT measurement. On the contrary, ifthe measurement duration has not elapsed at step 650, UE waits for thenext sampling cycling and returns to step 620.

Embodiment 3

The embodiment is implemented in such a way that the size of timeinformation field is fixed and the time stamp unit is set to be variableaccording to the measurement duration. Since the size of timeinformation field is fixed, the time stamp unit must be adjusted inorder to express all time during the measurement duration. Since thetime stamp unit varies according to the measurement duration, it cannotbe set to be identical to the sampling cycle. If the size of timeinformation field is set to a relatively small value, since the timestamp unit can express a relatively large span of time with respect to alarge measurement duration, times cannot be expressed in detail by thedifference. Therefore, the time information field is needed to be setwith an appropriate size at the initial stage. The time stamp unit canbe calculated based on the size of the time information field and themeasurement duration via the following equation 2.Time stamp unit=measurement duration/2x.Where the symbol x denotes the size of time information field(bits).  Equation 2

For example, as shown in FIG. 7, when the size of time informationfield, x, is 8 bits; measurement duration is 3600 seconds; and samplingcycle is 2.56 seconds, the time stamp unit is 14.0625 seconds(=3600/2.56).

If a log time of the 6^(th) sample 700 is derived, it is the 2^(nd)sample at time stamp=1.

Therefore, Relative time={floor [(14.06/2.56), 1]+}*2.56=17.92 seconds.

Therefore, the log time of a sample can be derived via the following,generalized equation 3.Relative time of the sample={floor(relative timing unit*Timestamp/sampling cycle)+position}*sampling cycle   Equation 3

The time stamp unit can be calculated in eNB or UE. This is because enBprovides the size of time information field and the measurement durationto the UE. Therefore, UE and eNB can have information for calculatingthe size of time information field. Thus, eNB can calculate the size oftime information field and inform UE of it. Alternatively, UE cancalculate the size of time information field via correspondinginformation transmitted from eNB.

In order to easily calculate a sample log time, the time stamp unit canbe expressed as the multiples of a sampling cycle. That is, the timestamp unit can be determined as the following equation 4.Time stamp unit=Ceiling(measurement duration/sampling cycle)/2x  Equation 4

Log time of a sample can be calculated as the following equation 5.Relative time of the sample=(time stamp*relative timeunit+position)*sampling cycle   Equation 5

For example, as shown in FIG. 8, when the size of time informationfield, x, is 8 bits; measurement duration is 3600 seconds; and samplingcycle is 2.56 seconds, time stamp unit=Ceiling (3600/2.56)/256=6sampling cycles.

If a log time of the 6th sample 800 is derived, it is the 1^(st) sampleat time stamp=1.

Therefore, Relative time=[6*1+1]*2.56=17.92 seconds.

FIG. 9 illustrates a flow chart describing a method for operating UE inembodiment 3 of the invention.

UE receives echoed absolute time, measurement duration, and samplingcycle from eNB via MDT configuration information (900). UE determinesthe time stamp unit, via equation 2, by using the measurement durationand the size of the time information field (905). It is preferable thatthe size of time information field is fixed and the UE and eNB havealready known the size.

Although the embodiment is implemented in such a way that UE calculatesthe time stamp unit, it can be modified in such a way that eNBcalculates the time stamp unit and provides it to the UE.

UE switches the current mode to an idle mode and performs MDTmeasurement (910). UE determines whether the sampling cycle arrives(915). If a time point arrives to log the measurement result at step915, UE collects information items to be logged in samples via thefollowing steps 920 to 935. Since steps 920 to 935 are identical tosteps 515 to 525 in FIG. 5, the detailed description is omitted. If theMDT measurements are logged according to a specific event, UE maydirectly perform step 920 without performing step 915.

UE logs the time stamp information in the time information field (940),and the last collected MDT measurement in one sample (945). UEdetermines whether the measurement duration has elapsed (950). If themeasurement duration has elapsed at step 950, UE stops the MDTmeasurement. On the contrary, if the measurement duration has notelapsed at step 950, UE waits for the next sampling cycling and returnsto step 920.

Embodiment 4

In order to reduce overhead in the time information field, if an eventoccurs where the time difference between samples isn't a sampling cycle,the time stamp values are inserted into samples instead of adding timestamps to all samples. This is because time can be predicted based onthe previously received samples as long as the sampling cycle has beenknown. However, embodiment 4 can be applied to only periodic pilotmeasurements logging MDT measurements at each sampling cycle, and thetime stamp value must be applied to the event-triggered log.

FIG. 10 illustrates a flow chart describing a method for operating UE inembodiment 4 of the invention.

UE determines whether the log sample is the first sample after MDT isconfigured (1000). If UE ascertains that the log sample is the firstsample at step 1000, it attaches a time stamp to the sample (1005). Onthe contrary, if UE ascertains that the log sample isn't the firstsample at step 1000, it determines whether the time difference betweenthe previous sample and the current sample is identical to the samplingcycle (1010). If UE ascertains that the time difference between theprevious sample and the current sample isn't identical to the samplingcycle at step 1010, it attaches a time stamp to the current sample atstep 1005. On the contrary, if UE ascertains that the time differencebetween the previous sample and the current sample is identical to thesampling cycle at step 1010, it doesn't attach a time stamp to thecurrent sample (1015).

FIG. 11 illustrates a schematic block diagram showing UE according to anembodiment of the invention. UE collects a global cell ID of a servingcell, RSRP/RSRQ, and location information via measuring units 1110, 1115and 1120, respectively, from signals via a transceiver 1100. If UE isequipped with a receiver for receiving satellite signals such as GPSsignals, the location measuring unit 1120 collects location informationfrom the received satellite signals. On the contrary, if UE isn'tequipped with a satellite signal receiver, it collects information,e.g., physical cell ID and RSRP/RSRQ of the adjacent cells, therebypredicting the location information. If the collected information istransferred to the controller 1105, the controller 1105 controls themeasuring units, calculates time stamps, and configures the finalsample. The controller 1105 receives corresponding information from eNBvia the transceiver 1100, in order to log time stamp values.

The controller 1105 configures time stamps, according to the sizes oftime information field and time stamp units that are have variable orfixed values, and performs control operations to log the measuredwireless channel information according to the configured time stamps.

In embodiment 1 as described above, the controller 1105 determines, ifthe time stamp unit and the size of time information field are fixed,whether the current time stamp information can be expressed with thesize of time information field. If the current time stamp informationcan be expressed with the size of time information field, the controller1105 logs the time stamp information in the time information field. Onthe contrary, if the current time stamp information cannot be expressedwith the size of time information field, the controller 1105 resets thelatest time stamp information.

In embodiment 2 as described above, the controller 1105 determines, ifthe time stamp unit is fixed and the size of time information field isvariable, the size of time information field, based on the measurementduration transmitted from eNB and the determined time stamp unit. Inparticular, the controller 1105 determines the size of time informationfield via equation 1.

In embodiment 3 as described above, the controller 1105 determines, ifthe time stamp unit is variable and the size of time information fieldis fixed, the time stamp unit, based on the measurement durationtransmitted from eNB and the determined size of time information field.In particular, the controller 1105 determines the time stamp unit viaequation 2.

In embodiment 4 as described above, the controller 1105 inserts timestamp information into samples if the time difference between one ormore samples where wireless channel information is logged doesn't matchthe sampling cycle.

Samples logging MDT measurements and time stamps are stored in a buffer(storage unit) 1125 of UE. When UE operates in a connected mode, UEinforms eNB that UE has stored MDT measurements. eNB requests the reportof MDT measurements from the UE if necessary. If UE receives therequest, the controller 1105 controls the buffer and transmits thestored MDT measurements to the eNB.

As described above, the UE according to the invention can effectivelyreport MDT measurements to a serving base station.

What is claimed is:
 1. A method for transmitting a message by a terminalin a wireless communication system, the method comprising: receiving,from a first base station, measurement configuration message includingabsolute time information associated with the first base station,logging interval information, and logging duration information; loggingmeasurement information periodically based on the logging intervalinformation until a timer identified based on the logging durationinformation expires, while the terminal is in a radio resource control(RRC) idle mode; receiving, from a second base station, a report requestmessage indicating a request of logged measurement information, whilethe terminal is in a RRC connected mode after transitioning from the RRCidle mode to the RRC connected mode; and transmitting, to the secondbase station, a measurement report message in response to the reportrequest message, the measurement report message including the absolutetime information associated with the first base station and a list oflogged measurement information including at least one periodicallylogged measurement information, wherein each of the at least oneperiodically logged measurement information includes relative timestamp, location information, cell identity information, reference signalreceived power (RSRP) information and reference signal received quality(RSRQ) information, wherein the relative time stamp indicates a time oflogging measurement result and is measured relative to the absolute timeinformation, and wherein the relative time stamp includes fixed sizebits indicating a value in seconds.
 2. The method of claim 1, whereinthe logging duration information is indicated by fixed size bits.
 3. Themethod of claim 1, wherein the logging duration information isindependent of state changes.
 4. A terminal in a wireless communicationsystem, the terminal comprising: a transceiver configured to transmitand receive a signal; and a controller configured to: receive, from afirst base station, measurement configuration message including absolutetime information associated with the first base station, logginginterval information, and logging duration information, log measurementinformation periodically based on the logging interval information untila timer identified based on the logging duration information expires,while the terminal is in a radio resource control (RRC) idle mode,receive, from a second base station, a report request message indicatinga request of logged measurement information, while the terminal is in aRRC connected mode after transitioning from the RRC idle mode to the RRCconnected mode, and transmit, to the second base station, a measurementreport message in response to the report request message, themeasurement report message including the absolute time informationassociated with the first base station and a list of logged measurementinformation including at least one periodically logged measurementinformation, wherein each of the at least one periodically loggedmeasurement information includes relative time stamp, locationinformation, cell identity information, reference signal received power(RSRP) information and reference signal received quality (RSRQ)information, wherein the relative time stamp indicates a time of loggingmeasurement result and is measured relative to the absolute timeinformation, and wherein the relative time stamp includes fixed sizebits indicating a value in seconds.
 5. The terminal of claim 4, whereinthe logging duration information is indicated by fixed size bits.
 6. Theterminal of claim 4, wherein the logging duration information isindependent of state changes.
 7. A method for receiving a message by afirst base station in a wireless communication system, comprising:setting measurement configuration message including absolute timeinformation associated with the first base station, logging intervalinformation, and logging duration information; and transmitting, to aterminal, the measurement configuration message, wherein the measurementinformation is logged periodically based on the logging intervalinformation until a timer identified based on the logging durationinformation expires, while the terminal is in a radio resource control(RRC) idle mode, wherein a report request message indicating a requestof logged measurement information is transmitted, from a second basestation to the terminal, while the terminal is in a RRC connected modeafter transitioning from the RRC idle mode to the RRC connected mode,wherein a measurement report message is transmitted, from the terminalto the second base station, in response to the report request message,the measurement report message including the absolute time informationassociated with the first base station and a list of logged measurementinformation including at least one periodically logged measurementinformation, wherein each of the at least one periodically loggedmeasurement information includes relative time stamp, locationinformation, cell identity information, reference signal received power(RSRP) information and reference signal received quality (RSRQ)information, wherein the relative time stamp indicates a time of loggingmeasurement result and is measured relative to the absolute timeinformation, and wherein the relative time stamp includes fixed sizebits indicating a value in seconds.
 8. The method of claim 7, whereinthe logging duration information is indicated by fixed size bits.
 9. Afirst base station in a wireless communication system, the first basestation comprising: a transceiver configured to transmit and receive asignal; and a controller configured to: set measurement configurationmessage including absolute time information associated with the firstbase station, logging interval information, and logging durationinformation, and transmit, to a terminal, the measurement configurationmessage, wherein the measurement information is logged, by the terminal,periodically based on the logging interval information until a timeridentified based on the logging duration information expires, while theterminal is in a radio resource control (RRC) idle mode, wherein areport request message indicating a request of logged measurementinformation is transmitted, from a second base station to the terminal,while the terminal is in a RRC connected mode after transitioning fromthe RRC idle mode to the RRC connected mode, wherein a measurementreport message is transmitted, from the terminal to the second basestation, in response to the report request message, the measurementreport message including the absolute time information associated withthe first base station and a list of logged measurement informationincluding at least one periodically logged measurement information,wherein each of the at least one periodically logged measurementinformation includes relative time stamp, location information, cellidentity information, reference signal received power (RSRP) informationand reference signal received quality (RSRQ) information, wherein therelative time stamp indicates a time of logging measurement result andis measured relative to the absolute time information, and wherein therelative time stamp includes fixed size bits indicating a value inseconds.
 10. The first base station of claim 9, wherein the loggingduration information is indicated by fixed size bits.